Solid ammonium hydrogen sulphide decomposes according to the equation NH4HS(s)⇌NH3(g)+H2S(g) at 25°c.  If the total pressure at equilibrium is 0.5 atm, the equilibrium constant Kp is

The given reaction belongs to heterogeneous equilibrium, in which gaseous products are always formed in equal number of moles. So, partial pressures of gases  PNH3=0.25 atm and PH2S=0.25 atm ∴Kp=PNH3PH2S=0.0625 atm2